Heretofore, it has been contemplated to improve the quality of images displayed, for example, in a CRT. One approach for this purpose is to produce a quasi-video signal corresponding to an intermediate scanning line between two adjacent or rather neighboring scanning lines. The quasi-video signal is produced through an interpolation processing based upon the video signals corresponding to the two neighboring scanning lines. The ordinarily performed interpolation processing is such that an average value of the video signals between the neighboring scanning lines is computed to provide the quasi-video signal corresponding to the intermediate scanning line therebetween. Although the displayed image is fine as a whole, it gives a feeling of disorder to the viewer due to the fact that the quasi-video signal thus produced, is not derived from the real image.
U.S. Pat. No. 4,774,581 (Shiratsuchi) discloses an electronic circuit system for magnifying a video image to have the effect of a zoom lens by adding a value N to a stored N value in accordance with a modulo M operation to obtain a new stored value. The result is a magnification of the video image by a factor of M/N relative to the original unmagnified image. The determination of the magnification factor with the value N according to Shiratsuchi is not determined by the luminescence data of two neighboring pixels that are spaced from each other diagonally. Shiratsuchi interpolates along adjacent lines and does not teach any interpolation by a convolution operation.